1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus of the electrostatic type which converts image information printed on a document into an electronic image and then renders the information visible, thereby copying the image information.
2. Description of the Related Art
Various image forming apparatuses are known which perform an electrophotographic copying process, for example, a copying machine or a printer apparatus. The copying machine or printer apparatus includes: an image reading section for illuminating an image formed on a document; an image forming section for receiving the light reflected from the document, forming an electrostatic latent image from the light, and reproducing the image from the electrostatic latent image; and a material delivering section for supplying material, such as a plain paper sheet or an OHP sheet, to the image forming section, and for delivering the sheet after the image has been reproduced on the sheet.
The image reading section has a document table for supporting a document, an illuminating device for illuminating the document, and an optical unit for applying the light, reflected from the document, to the image forming section.
The image forming section has a cylindrical photoconductor, a charging device, a developing device, a transferring unit, a fixing unit, and a clearing device. The photoconductor rotates to form an electrostatic latent image which corresponds to the light reflected from the document. The charging device is used to apply an electric charge to the photoconductor. The developing device forms a visible image from the electrostatic latent image formed by the photoconductor. The transferring device is designed to transfer the visible image from the photoconductor onto the sheet. The fixing unit is designed to fix the visible image on the sheet. The cleaning device is used to change the charge distribution of the photoconductor to an initial change.
The material delivering section has paper cassettes, a paper feeder, and an outputting unit. The paper cassettes are used to contain paper sheets onto which images are to be transferred. The paper feeder is designed to feed the sheets from the cassettes to the image forming section. The outputting unit is designed to deliver the sheets, with images fixed on them, from the image forming section.
In the copying machine described above, the charging device applies a predetermined charge to the photoconductor. The light reflected from the document is applied to the photoconductor, by means of an optical unit which has a plurality of mirrors and a plurality of lens elements, thereby forming an electrostatic latent image on the periphery of the photoconductor. The electrostatic latent image corresponds to the image formed on the document. The developing device applies a developing agent, such as toner, onto the periphery of the photoconductor, thus converting the latent image to a visible image. (More specifically, the visible image known as "toner image" is transferred to the paper sheet). The toner image is transferred from the photoconductor to a paper sheet by the transferring device and then fixed on the paper sheet by the fixing unit. Then, the toner forming this image is heated and, in some case, compressed, thus fixing the toner image. The paper sheet, with the toner image thus fixed on it, is delivered from the image forming section.
The image forming apparatus of the type described above can operate in various copying modes, such as a photography mode and a color change mode. Whatever mode the operator has selected, the apparatus operates, producing a hard copy. For example, when the apparatus operates in the photography mode, it produces a hard copy having a mild contrast; when it operates in the color change mode, it produces a hard copy in a selected color, not a back-and-white hard copy.
The conventional image forming apparatus is, however, disadvantageous in the following respect. Once it has started a copying process, it cannot operate in a new mode or under new conditions, up until it finishes the copying process. In other words, to operate the apparatus in a new mode or under new conditions, the operator must wait until the apparatus completes the copying process being performed. Hence, toner and paper are inevitably wasted, increasing the copying time and cost.